Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $188.36   8.279%   $203.9543   $203.95   $203.95   $204.00  
  Purchase #2 $179.39   11.661%   $200.3087   $200.31   $200.30   $200.30  
  Purchase #3 $111.57   13.685%   $126.8384   $126.84   $126.85   $126.80  
  Purchase #4 $208.78   7.744%   $224.9479   $224.95   $224.95   $224.90  
  Purchase #5 $71.56   8.731%   $77.8079   $77.81   $77.80   $77.80  
  Purchase #6 $57.95   11.421%   $64.5685   $64.57   $64.55   $64.60  
  Purchase #7 $168.70   8.330%   $182.7527   $182.75   $182.75   $182.80  
  7 purchase totals = $986.31       $1,081.1784   $1,081.18   $1,081.15   $1,081.20